1. Field of the Invention
The present invention relates to a package structure. More particularly, the present invention relates to an anti-warp package and method of fabricating the same.
2. Description of the Related Art
The semiconductor packaging process can be roughly subdivided into a series of individual steps including wafer sawing, chip attaching, wire bonding, molding, printing and packaging. Molding is one of the processing steps whose purpose is to provide a barrier to the penetration of moisture, a medium for transferring internally generated heat away, a suitable shape for handing and insulate the internal electrical devices from external electrical devices. In general, the molding process comprises placing a substrate having semiconductor chips or electronic devices thereon inside a mold, heating some solid epoxy molding compound to a liquid form and injecting the liquid compound into the mold cavities inside the mold by applying a pressure through a plunger. Ultimately, the molding compound encapsulates the semiconductor chips or electronic devices on the substrate to form an airtight package. After the molding compound is cured, the package is released from the mold.
To produce packages en-mass, a plurality of semiconductor chips or electronic devices are disposed on a packaging substrate and encapsulated all at the same time. Thereafter, the packaging substrate is sawed to produce a plurality of independent package units. However, the material of the molding compound used for encapsulating and the material of the packaging substrate normally have different coefficient of thermal expansion. Thus, the degree of expansion or contraction between the packaging substrate and the molding compound as the temperature variation during the curing process may create stress that leads to a warping of the packaging substrate. As a rule, the higher the curing temperature and the longer the curing time, the greater will be the degree of warping in the packaging substrate so that the packaging substrate is more difficult to saw. Furthermore, because the semiconductor chips and the electronic devices are bonded to the packaging substrate, any warping stress within the package may be transmitted to the semiconductor chips or the electronic devices as a bending torque as well. If the bending torque is too large, the semiconductor chips or the electronic devices can be damaged.
However, for an optical device having the aforementioned package structure such as a land grid array (LGA) package structure, the degree of warping in the packaging substrate could be substantially increased because a transparent resin must be used as the molding compound. In general, the degree of warping in the packaging substrate is increased because the coefficient of thermal expansion of a transparent packaging resin is higher than most non-transparent packaging resin. Thus, it is necessary to provide a packaging substrate having a structure capable of minimizing warping after molding.